Conventionally, a technology called “snapshots” is known as a method for extracting image data from a logical volume in operation at a certain point in time (hereinafter referred to as the “operation volume”). By means of this snapshot technology for example, when receiving a write request from a host system, the storage apparatus updates data in accordance with this write request after saving only pre-update data from the operation volume to another logical volume (hereinafter referred to as the “snapshot volume”). Subsequently, the storage apparatus updates the data in the operation volume based on the write request.
Therefore, the snapshot technology can achieve access to data at a plurality of certain points in time and further achieve such access by using small capacity.
Now, Patent Literature 1 discloses a storage apparatus and its control method for performing control so that if an access request is made to a snapshot volume to which data is saved by a snapshot, data which is not saved is obtained from a duplicate of the operation volume (hereinafter also referred to as the “duplicated volume”). Subsequently, Patent Literature 1 indicates that the acquisition of data from the operation volume as much data as obtained from the duplicated volume can be inhibited and the access load on the operation volume can be reduced.